Cut back tall perennials to keep them looking great

As you can see by the title this column is all about shearing and how taking time to do it will keep garden plants from doing a face plant in late summer. But first, I want to send out a little public service announcement. As you may know, when shopping for perennials you want to look for plants marked as being hardy in our unbelievably cold Zone 4 (-30 degrees F) climate. Otherwise, you can’t count on seeing them the following year.

Some gardeners are willing to take a chance on a Zone 5 plant they really love like Japanese maple, say, or butterfly bush, figuring if it dies it dies but if it lives — great! But you shouldn’t have to take a risk if you don’t want to, and that’s exactly what’s happening when we buy plants with misleading tags. Truthfully, no season goes by that I don’t see some mislabeled plants at garden centers, even really good ones. But this year I’ve been hearing from many gardeners that there are a LOT of mislabeled plants out on shelves, particularly at big-box stores where plants are often shipped in from the South. 



What can you do? If you don’t know for sure whether a perennial is hardy in Minnesota (Zone 4 or lower) and you’re at an actual garden center rather than a big-box store, ask someone to confirm the zone. All good garden centers have reference books behind the counter. If you find a plant labeled Zone 4 that you always thought we couldn’t grow here, you probably can’t. To ensure you don’t throw money away on plants when you aren’t sure of the zone, buy from places that offer at minimum a one-year guarantee and keep your receipt. It’s a buyer beware world out there so shop wisely.



Shearing, not deadheading



I’ve written about deadheading in the past and many of you probably already do it, right? When blooms are spent you pinch them off (deadhead) to encourage new blooms. That’s about it. Shearing, though, is an entirely different thing and many gardeners, including me, don’t do this nearly enough. Less work than pruning, shearing means you get yourself a pruner or hedge shears and cut back perennials that tend to get far too gangly by late summer like tall asters, coneflowers, prairie ironweed, some types of goldenrod, bee balm, boltonia, Joe Pye weed and Russian sage.

For early summer bloomers, shear toward the beginning of the season so you’re not cutting off flower buds. (It’s fine to shear after flower buds set, but depending on the plant you may not get blooms in the same year.) With the cold weather this year mid-June is probably a good time, but you may want to go a bit longer. Cut plants back to about half. That way when they bloom they’ll be at a much more manageable height and they won’t flop over into the dirt whenever a strong wind or rain whips through. Cutting plants back to half also helps eliminate that ugly open space you often see in the center of tall plants.

Wait until late June to shear late-blooming plants like asters and goldenrod. And as you shear, cut out any parts of the plant that have become brown or damaged as summer progressed. Again, shear back to one-third or half the perennial’s size. In addition to more manageable height, another positive effect you’ll notice after shearing is that you often encourage branching so plants fill out and look more shapely rather than just being tall and stick-like.

Many good reasons to shear



Even with perennials that don’t tend to topple over, shearing is a great way to maintain the height of certain plants in the garden or to improve their appearance since many perennials get ratty looking as the summer goes on. Shearing back perennials allows you to delay blooming, for example. This can be a good thing if you have several plants of the same type in a group and you’d like to stagger the blooms in order to have more color in the garden, longer. You can even keep one plant in bloom longer by cutting back select stems rather than all of them at the same time.

Shearing also promotes reblooming of many perennials. Some early spring perennials, such as candytuft and creeping phlox, will bloom again if you shear them immediately after the first round of flowers are spent. Some summer bloomers that will reflower after a shearing are yarrow, catmint, salvia, bee balm, tickseed and cranesbill (geranium).

If you feel a little confused, don’t worry. The worst thing that’s going to happen if you shear something that doesn’t benefit all that much from shearing is that it’ll be short and perhaps not bloom for a year. You’ll learn as you go, and you’ll be amazed by how much better your perennials look when you shear them rather than allowing them to just do their own, wild thing.

This post originally appeared in the Southwest Journal.